In most cases, erythromycins, which are used in chemotherapy for various bacterial infections, are orally administered. When these compounds are to be administered via internal use, the characteristic bitterness thereof makes it necessary to formulate them into capsules or coated tablets. For-those who cannot smoothly swallow down these drugs such as children and aged persons, however, it is desirable to formulate these compounds into solutions or granules. In these cases, the bitterness cannot be fully relieved by simply masking them. In order to solve these problems, attempts have been made to develop various esters which show no bitterness at the administration but return into the original active compounds at or after the absorption in vivo.
Examples of these esters include erythromycin ethylsuccinate [Antibiotics and Chemotherapy, 7 (9), 487 (1957).sub.], erythromycin propionate lauryl sulfate [Journal of the American Pharmaceutical Association, .48 (11), 620 (1959)], allyl, ethyl and benzyl carbonates of erythromycin [Antibiotics Annual, 1953-1954, 500 (1954)]and 2'-ester of O-methylerythromycin derivative (JP-A-61-200998).
However these known compounds are generally insufficient in absorbability in vivo. Further, these compounds per se generally have a weak antibacterial activity. Therefore, they should be rapidly converted into the original active compounds in vivo. However, these compounds are hardly converted into the original active compounds in vivo in practice, which makes it impossible to achieve satisfactory therapeutic effects.